This invention relates to matrix addressable display devices, and more particularly to a method for testing the emission of the displays.
Quality assurance requires the testing of manufactured products to determine if they will function over a given set of parameters. Testing is performed on a random sampling of products from the production lines, or in some industries, on every product which is manufactured.
Optical measurements are currently performed on display devices at the final stages of display testing. Optical measurement is accomplished by turning on all the cathode emitters in a pixel, and visually observing them. This method is extremely subjective, as it relies on the judgement of the individual peering at the screen.
Photon Dynamics of Milipitas, Calif. employs a method in which photons from a full display (i.e., substantially all of the pixels are turned xe2x80x9conxe2x80x9d at the same time) are measured. A completed display device is optically tested by measuring the light emitted from the display.
There are several drawbacks to the above described optical method. For example, the process is very expensive, as it requires sophisticated optics and processing algorithms in order to determine the relative number of functional pixels.
Additionally, the optical systems require closely spaced anodes with respect to the cathode in order for the inspection optics to obtain accurate measurements. Therefore, the optical systems are not practical for testing display base-plates prior to their assembly in a field emission device.
Other methods used to measure current emitted by field emitter devices employ a positively biased electrode. However, these methods also measure the total current emitted by substantially all of the pixels in the completed unit. Therefore, these methods are also limited to measuring the operation of the device as a whole.
There still exists a need for a method to measure the current emitted by individual pixels in the display in order to determine their functionality, as well as the total number of functioning pixels (also known as the xe2x80x9cyieldxe2x80x9d). Additionally, manufacturing realities require that the functionality of the individual pixels is measured in a rapid fashion.
The functionality of individual pixels in an addressable emissive cathode is determined by measuring the emitted current from a single pixel or from a small group of pixels. The current is measured on an anode screen disposed above the cathode emitters, thereby enabling the anode to collect electrons emitted from the cathodes. The collected current is compared to known parameters in order to determine whether the individual pixel site is functional.
The method of the present invention allows for the testing of cathode emitters in a vacuum chamber through the use of probe cards or sockets, and an anode. This format allows for the testing of approximately 100,000 pixels in less than 30 seconds, thereby expanding testing capabilities. Not only does the present technique permit faster testing, but also a less expensive alternative to the functionality tests used for individual pixels.
One advantage of the test method of the present invention is that it enables rapid determination of individual pixel functionality of the cathode emitters used in field emission type displays, or other similarly addressed matrix displays. For example, the present test method is suitable for displays that are actively or passively addressed.
The method of the present invention permits testing of the cathode emitters either as a baseplate or an assembled display device. Additionally, the use of an anode which luminesces under electron bombardment permits the measurement of emitted photons to determine pixel functionality.
The present invention is employed to sequence through all of the pixels, one or more at a time. Additionally, there is no required spacing for the anode in order to achieve accurate measurement. Further the present invention can be used with current optical methods to enhance the value of those methods.
One embodiment of the present invention is a method of testing cathode emitters by measuring the current emitted from the emitters. A group of cathode emitters comprises a pixel.
Another embodiment of the present invention is a method for measuring functionality in an addressable matrix used in a display device by addressing a single pixel, thereby creating an output. The output of the single pixel is then measured to determine functionality of that particular pixel.
A further embodiment of the present invention is a method for determining functionality of cathode emitters in which at least one pixel is addressed, thereby producing a current. The pixel is comprised of at least one cathode emitter. Collecting the current using an anode which is disposed opposite said at least one pixel. Measuring the current, and comparing the current to an expected value.